Cross Backstage
From A3! Wiki
Cross Backstage (クロスバクステ) is a story between two characters which can be read when you have obtained any SSR of each character. The only exception currently is Banri and Tsumugi's Cross Backstage "CAFE LazyTime" which requires the specific SSR cards from the February Magic bitter & sweet limited scout. Only one of the two SSRs is required to unlock the story. Reading a Cross Backstage for the first time grants 15 Dias.
